Lipid nutrition in haddock (Melanogrammus aeglefinus) and Atlantic cod (Gadus morhua): The role of dietary lipid in hepatic lipid deposition

It is known that gadoid fish store the major proportion of unused dietary energy as lipid in the liver. In farmed gadoids, total liver lipid levels can reach >70% when fed diet containing >14% lipid. This condition is often referred to as fatty liver syndrome. However, total muscle lipid (generally at levels less than 1%) is not affected by higher dietary lipid intake. Observations from culture facilities indicate that the fatty liver affects the overall health and growth of the fish. The focus of this research is to determine factors that could possibly minimize the prevalence of fatty liver syndrome in haddock (Melanogrammus aeglefinus) and Atlantic cod (Gadus morhua);Juvenile Atlantic cod were fed diets containing graded levels of cholesterol (0-4%) for 12 weeks. Hepatosomatic index and total liver lipid content were reduced in fish fed 4% cholesterol. While not affecting muscle and heart cholesterol content, up to 2% dietary cholesterol increased deposition of cholesterol in the liver. Further studies to elucidate the mechanism by which cholesterol acts to lower hepatic lipid deposition in gadoid fish are warranted.;Juvenile haddock fed a diet containing conjugated linoleic acid exhibited lower growth and green discolouration of the liver in 85% of the fish. Histology of the hepatic tissue revealed necrosis, lipid peroxidation and bile duct hyperplasia. Haddock fed a diet containing cholesterol showed an increase in growth and a reduction in liver lipid deposition over 9 weeks. Replacement of herring oil with 2% cholesterol resulted in increased growth and a reduction in hepatosomatic index.